diff --git a/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php b/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php
index 81810f7..d9df046 100644
--- a/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php
+++ b/core/tests/Drupal/FunctionalTests/BrowserTestBaseTest.php
@@ -99,7 +99,7 @@ public function testForm() {
     // Test drupalPostForm().
     $edit = ['bananas' => 'red'];
     $result = $this->drupalPostForm('form-test/object-builder', $edit, 'Save');
-    $this->assertInternalType('string', $result);
+    $this->assertSame($this->getSession()->getPage()->getContent(), $result);
     $value = $config_factory->get('form_test.object')->get('bananas');
     $this->assertSame('red', $value);